The present invention relates generally to apparatus and methods for producing pressurized water, and more particularly to a high-pressure water pump for supplying high pressure water to an evaporative cooling apparatus and particularly to so-called fogging nozzles for cooling the inlet air of a gas-turbine generator.
Existing fogging systems for evaporative coolers utilize crankshaft based reciprocating piston or gear type water pumps to create high pressure water (1500 to 3000 psi) which is atomized by known forms of fogging nozzles in the inlet airstream of a gas turbine to cool the inlet air. High pressure water is required to achieve the small droplet sizes needed to insure that the droplets completely evaporate prior to their entrance into the turbine inlet.
In gas turbine fogging systems it is common to use de-ionized water to prevent mineral contamination downstream and on turbine parts; thus all coated components, including the pump, must be of stainless steel and exotic seal materials. This type of equipment calls for maintenance on weekly intervals. Moreover, only a limited number of suppliers produce reliable high pressure de-ionized water pumps. Due to this limited supply and the nature of the materials required to make these pumps they are quite expensive.
Moreover, with the prior art pumping systems, in order to achieve volume control, pressure relief valves are used to redirect water back to the pump. This causes heating of the water which reduces its evaporative efficiency and increases pump wear.
For large systems, and in order to vary the water volume, several pumps are required and the water not used immediately will be recirculated from the pressure side of the pump(s) back to the pump inlet. To have several pumps providing a required volume of high pressure water plus control mechanisms adds further to the water temperature, since some of the energy driving the pump inevitably gets added to the water. The water temperature will thus rise well above the wet bulb temperature, further decreasing the cooling efficiency of the water.
The present invention presents new and unique methods and apparatus for providing a constant high pressure water stream to the atomizing spray nozzles used for evaporative cooling of the inlet air of a gas-turbine generator.
In accordance with an aspect of the present invention, a hydraulic pump system is provided with a variable stroke, axial piston pump (or other variable volume pump) which supplies a high pressure oil flow to drive one or more hydraulic cylinders which in turn drive pistons in one or more water cylinders to pressurize water and supply it to the spray or fogging nozzles.
The water cylinders may be of single or double acting type and produce water pressure between 0-10,000 psi, and preferably between 1000-5000 psi.
An advantage of the present invention is that the system maintains a substantially constant water pressure range as the volume varies from zero to maximum water flow. Moreover, the power consumed by the hydraulic pump varies directly with the output of the pump.
Another advantage of the present invention is that the efficiency of the hydraulic water pump system at full flow is equal to or better than prior art devices, and increases at reduced flow.
Yet another advantage of the present invention is that staging does not require multiple hydraulic systems and controls. The output of one large hydraulic system can be divided into as many stages as required. Backup systems may be also used as a redundancy measure.
The present invention includes the ability to vary the amount of water fogged into the air stream using as many stages as desired, there being theoretically no limit to the number of stages used. The stages are created using valves, and provide the coarse adjustment of the humidification. The pressure output of the hydraulic pump is varied over a preset range to vary the volume of water delivered. This can be controlled by a programmable logic controller (PLC) through a milliamp output based on the difference between the wet bulb and dry bulb temperatures of the ambient air.
In atomizing spray evaporative cooling systems used to improve operations of gas turbines, the amount of water to be sprayed into the air must be tightly regulated in order to achieve maximum efficiency. First the air temperature, humidity and barometric pressure are measured. Second the saturation water content of air at the measured temperature and pressure is calculated by known means. The difference between the ambient humidity and the saturation humidity is the maximum amount of water which may be evaporated into the air stream. As a result, the flow of water must be set as close to this value as possible in order to achieve the maximum cooling and thus maximum increase in turbine output performance. Alternately, additional water may be added to the air stream in order to provide inter-cooling for the turbine. In either case, the precise amount of water to be added is determined empirically, and must be closely controlled.
The hydraulic system of the present invention is inherently a variable volume device. Thus the water flow rate can be set by simply selecting the number of spray heads to be activated and the outlet pressure supplied by the water cylinders. However, the system allows fine tuning of the water flow through adjustment of the water pressure, which is easily achieved through adjusting the hydraulic pressure using standard pressure control techniques (e.g., proportion flow control devices on the hydraulic oil lines, pump speed control, or pressure relief control, etc.). Moreover, by utilizing hydraulic oil pumps, not only is reliability and durability significantly improved, but cost of components is significantly reduced.
A high-pressure water pump in accordance with the present invention for supplying high pressure water to the fogging or atomizing nozzles used to cool inlet air for a gas-turbine generator includes a first hydraulic oil cylinder having a piston and a connecting rod having a first end attached to one side of the piston. The connecting rod includes a second end protruding out a first end of the cylinder. The hydraulic cylinder also includes a first port arranged adjacent the first end of the cylinder in fluid communication with a first port of a solenoid valve, and a second port arranged adjacent a second end of the cylinder in fluid communication with a second port of the solenoid valve. The solenoid valve is in fluid communication with the high pressure line of a hydraulic oil pump and a return line of said hydraulic oil pump. The pump according to this aspect of the invention also includes a first water cylinder having a piston attached on one side to a second end of the connecting rod, with the second end of the connecting rod entering the cylinder through an opening in the first end of the water cylinder. In one embodiment the water cylinder is a single action cylinder having a first port arranged adjacent the first end of the water cylinder in fluid communication with a first check valve for allowing low pressure water to enter the cylinder, and a second, oppositely acting check valve connected to a second port for allowing water to be forced out of the second port by the piston and enter a high pressure water line. In another embodiment the water cylinder may be a double action cylinder capable of pumping water alternately from opposite ends under the control of appropriately arranged check valves.
In another aspect of the present invention, the above high-pressure water pump further includes pairs of hydraulic and water cylinders working together.